1. Field of the Invention
The present invention relates to a copying apparatus, and more particularly; to an electrophotographic copying apparaus employing a photoreceptor to form an electrostatic latent image of an original to be copied thereon, which latent image is subsequently developed into visible toner powder image to be transferred and fixed onto a copy paper sheet.
2. Description of the Prior Art
In general an electrophotographic copying apparatus has a photoreceptor having a photoconductor surface thereon, and an electrostatic latent image of an original is formed on it by projecting an optical image of the original thereon. Then, the latent image is transferred into a visible image of toner particles by utilizing developer, thereby the toner image is further transferred onto a surface of a copy paper sheet. The receptor is usually shaped as a drum which is journaled rotatably around its axis. The electrophotographic copying apparatus further operably comprises around the receptor a corona charging means for preliminarily charging said photoreceptor, an optical means for projecting the image of the original onto the surface of the photoreceptor, a developing means for developing a latent image on the photoreceptor of the original thereby to obtain a toner image, a transferring means for transferring the toner image onto a surface of copy paper sheet and a cleaning means for cleaning a residual toner image remaining after the transferring. The copying apparatus further comprises a copying paper feeding apparatus and a fixing means for fixing the toner image on the copying paper sheet. In order to project the image of the original onto the surface of the cylindrical photoreceptor, the optical means comprises an optical scanning device which scans the original to obtain a latent image of the linear part of the original which linear part moves vertically to the linear part. To perform the copying operation, the optical scanning means needs to move reciprocally, different from the single direction movings of the photoreceptor drum, the paper sheet feed-in means and a means to advance the paper sheet from the transferring means to the fixing means.
Hitherto, the electrophotographic copying apparatus has employed a single A.C. motor, for example a synchronous motor or an induction motor of a considerably large output power as a driving means for the motions of the abovementioned means, and a single direction motion of the motor is transmitted to the various means which require the single direction motions and a pair of electromagnetic clutches are used to obtain the reciprocation motions of the optical scanning means.
In such conventional copying apparatus, the photoreceptor drum and the optical scanning means have been driven by a common motor, in order to assure complete coincidence of surface speeds of the photoreceptor drum and the scanning of the original. The coincidence is necessary for accurate reproduction of the copied image, and without such coincidence the reproduced image becomes distorted, for example shortened or elongated. In order to obtain such coincidence, a chain transmission system, which accurately transmits the revolution from the common motor to the photoreceptor drum and the optical scanning means, has been used. In such conventional copying apparatus, for driving the revolutions of the photoreceptor, developing means, fixing means, copy paper sheet driving roller and optical scanning means, a considerably large A.C. motor having axial output power of such as 60-90 W is used. Furthermore, in order to produce reciprocation motion of the optical scanning means, a pair of electromagnetic clutches is necessary, and such electromagnetic clutches are generally expensive and consume consideable electric power.
In a second type conventional apparatus, in order to reduce the large power of the motor, a second A.C. motor has been used to drive the developing means which requires a considerable torque. In such apparatus, both the optical scanning means and the photoreceptor are driven by a first motor. Though a first motor and the second motor can be made smaller than the single motor of the first type conventional apparatus, the total of the volume and weight of the two motors of the second type conventional apparatus becomes larger than those of the single motor of the first type apparatus, and hence the use of two ordinary A.C. motors is not appropriate for a small and light type electrophotographic copying apparatus.
The A.C. motor such as the synchronous motor or the induction motor has a considerably high rotation speed such as 1800 rpm, and therefore, it is necessary to use a gear head having a reduction ratio of one several tenth inserted between the output shaft of the motor and the driven shafts of the abovementioned means and devices. Such gear head makes a considerable noise, besides the noises produced by the chains and sprocket therefor.
Furthermore, by attaching the gear head between the motor shaft and the driven devices, the totals of the length and space required for containing the combination of the motor and the gear head become large, and therefore, the housing of the copying apparatus becomes large.
Besides, use of the chain transmission system which connects the motor, electromagnetic clutches and various driven devices requires certain spaces in the housing, thereby increasing the volume and further makes the construction of the devices complicated, and assembling of the copying apparatus has been complicated because of the use of chain or belt transmission system.